1. Field of the Invention
The present invention relates to methods of forming a carbon-rich (spin-on carbon) layer from a polyamic acid for use in a multilayer stack and the microelectronic structures thereof.
2. Description of the Prior Art
As the semiconductor industry continues to shrink the size of features, a single layer photoresist lacks sufficient thickness to complete pattern transfer to a substrate. As a result, trilayer stacking (photoresist-hardmask-carbon layers) is typically used to transfer the pattern made by the photoresist to the substrate. The carbon layer can be formed by chemical vapor deposition (CVD) or spin-coating. However, CVD processes are expensive, have low-throughput, and subject the wafer to harsh conditions. Currently, epoxy cresol novolacs are the most common material for fabrication of spin-on carbon (“SOC”) layers, but this material has low thermal stability and low carbon content, leading to high sublimation and poor wiggling resistance during pattern transfer to silicon substrates. Additionally such a layer is difficult to remove after curing. Other SOC layers have been formed that are removable by dry etching. However, drying etching requires harsh processing conditions and special equipment, making the process less than desirable.
There is a need for improved SOC layers that exhibit high thermal stability and optical constants, while also being wet removable (developer soluble). Furthermore, these layers should prevent or minimize line “wiggling,” which is present in many prior art processes.